• add optional client field to publish API requests. client will be added on top level of
  published message. This means that there is now a way to include client connection ID to
  publish API request to Centrifugo (to get client connection ID call centrifuge.getClientId() in
  javascript). This client will be included in a message as I said above and you can compare
  current client ID in javascript with client ID in message and if both values equal then in
  some situations you will wish to drop this message as it was published by this client and
  probably already processed (via optimistic optimization or after successful AJAX call to web
  application backend initiated this message).
• client limited channels - like user limited channels but for client. Only client with ID used in
  channel name can subscribe on such channel. Default client channel boundary is &. If you have
  channels with & in its name - then you must adapt your channel names to not use & or run Centrifugo with another client channel boundary using client_channel_boundary configuration
  file option.
• fix for presence and history client calls - check subscription on channel before returning result
  or return Permission Denied error if not subscribed.
• handle interrupts - unsubscribe clients from all channels. Many thanks again to Mr Klaus Post.
• code refactoring, detach libcentrifugo real-time core from Centrifugo service.